In many existing wireless communication systems, such as for example, certain cellular communication systems, the transmit power levels from the mobile units to the base station of the systems are controlled. For example, in some multiple-access systems utilizing spread spectrum technology, power is controlled at each mobile unit in order to reduce interference caused by the transmissions of each mobile unit on the transmissions of the other mobile units using the same channel. Controlling the transmit power also helps to reduce power consumption at the mobile units, which are typically battery powered. Essentially, the transmission power of each mobile unit is set high enough so that signals are received at the base station at a desired Signal-to-Interference plus Noise Ratio (SINR), but low enough to meet the above-described goals of reduced interference and power consumption.
In order to determine the transmission power of each mobile unit, a SINR set point is established for the system involved. Generally, the SINR set point is based on the minimum data rate required by the system. In wireless communications, the maximum data rate of transmission between two mobile units is directly proportional to the SINR between the two units. A relatively low SINR limits the maximum data rate, because data received with a low signal-to-noise ratio requires a large amount of processing to extract the transmitted signal from the received waveform. Conversely, a relatively high SINR enables a high transmission data rate, because only a small amount of processing is required to extract the transmitted signal from the received waveform. Therefore, when a system establishes its SINR set point, the data rate required for proper throughput is determined and a minimum SINR is established to achieve the required data rate. A system SINR set point is then set at or slightly above this minimum SINR value. In many of the systems involved, the system set point is modified over time to account for changes in the number of users in the system and/or environmental phenomena.
Once a system's SINR set point is determined, the transmit power level for each mobile unit can be established so that a signal sent from a mobile unit is received by the base station at the SINR set point. Typically, this function is accomplished through feedback from the base station to each mobile unit regarding that mobile unit's received SINR. For example, when a mobile unit transmits a signal to the base station, the base station measures the SINR of the signal and either notifies the mobile unit of its SINR or directly commands the mobile unit to adjust its transmission power. In either case, the mobile unit sets its transmission power so that signals are received at the SINR set point. Different mobile units may be located at different distances from the base station. Consequently, different mobile units may transmit at different power levels in order to achieve the established SINR set point.
Generally, each mobile unit transmits at the minimum power level needed to achieve the SINR set point. This approach minimizes the amount of interference caused by each mobile unit on the signals of other mobile units. Also, by having the mobile units transmit at the minimum power level, the users of the mobile units can obtain the maximum usage (e.g., talk time, etc.) from their battery powered mobile units.
In certain wireless communication networks, such as for example, wireless cellular networks using Direct-Sequence Spread Spectrum (DSSS) modulation techniques, two types of power control are used to maintain system performance: (1) inner loop power control is used to ensure that all of the radio transceivers in the network can obtain links of similar quality; and (2) outer loop power control is used to degrade performance systematically when the network becomes overloaded. The existing power control techniques are suitable if the radio transceivers being used in a network have similar (or identical) operating characteristics or functions, such as for example, cellular phones or Blackberry wireless devices. However, a significant problem with the existing power control techniques is that there is no systematic technique currently available that can exploit the advantages of today's wireless radio transceivers that have different receive antenna saturation levels, different transmit power limits, and/or are capable of adjusting to wide variations in traffic (e.g., in military wireless networks). Therefore, a pressing need exists for a power control technique that can be used to exploit the technological advantages of existing (and future) wireless radio transceivers, and resolve the above-described problems and other related problems.